全文获取类型
收费全文 | 430篇 |
免费 | 67篇 |
国内免费 | 78篇 |
专业分类
化学 | 573篇 |
物理学 | 2篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 30篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 18篇 |
2016年 | 28篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 55篇 |
2012年 | 21篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 25篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 25篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
排序方式: 共有575条查询结果,搜索用时 15 毫秒
91.
Junfa Wei Zhanguo Chen Yanni Gao Peng Zhang Chuanning Wang Pengfei Zhao Yun Wang Xianying Shi 《中国化学》2012,30(2):391-399
The urea‐catalyzed aziridination of 1,2‐vicinal haloamines derived from aminohalogenation of olefins has been developed. This rapid and simple method was carried out by simply grinding the solid mixture of the substrate, K2CO3 and catalytic amount of urea at room temperature in air. The reaction provides a protocol for quantitative preparation of aziridines in a large scope of aminohalogenated derivatives of olefins including α,β‐unsaturated ketones, α,β‐unsaturated esters and simple olefins. The possible mechanism involving an H‐bond promoting deprotonation has been suggested for this reaction. 相似文献
92.
Hydroaminomethylation of various olefins with primary and secondary amines was carried out using a simple and efficient rhodium–phosphinite complex catalyst. The influence of various reaction parameters including the effects of temperature, pressure, catalyst loading, time and solvents has been investigated. The present protocol is general with wider substrate applicability for the synthesis of an important class of aliphatic amines and arylethylamines. High activity and selectivity for amines was achieved with a very good substrate/catalyst molar ratio (turnover number 2500) under mild reaction conditions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
93.
94.
95.
96.
97.
《中国化学快报》1998,(5)
Muchattentionhasrecentlybeenpaidtophotoassisted0rganicsynthesiswithhighyieldsandselectivitiesl'2.Theincreasingnumberofpapershaveshownthatthereisasubstantialinterestintheapplication0fph0t0chemicaltechniquestoh0mogeneouscatalysis.Well-knownexamples,whichshowthatlightcaninitiateandacceleratecatalyticreacti0ns,includephotocatalyzed0lefinisomerization',methoxycarb0nylati0n',andfunctiona-lizationoftheC-Hbondofalkanes5'6.Itiskn0wnthatmeth0xycarb0nylationofolefinsisanimp0rtantchemicalprocess,butitsap… 相似文献
98.
Hydrogenation reactions of olefinic hydrocarbons using ruthenium-incorporated pillared montmorillonite as catalysts are reported.
Depending on the steric hindrance, Ru/pillared montmorillonite selectively reduces carbon-carbon double bonds using hydrogen
under pressure. 相似文献
99.
Vijay Kumar 《Tetrahedron letters》2006,47(39):7001-7005
Highly selective and efficient Michael additions of heterocyclic enamines, viz. indoles, pyrroles, and pyrazoles with α,β-unsaturated olefins using 2 mol % of ZrCl4 has been achieved. 相似文献
100.
Alexander N. Tavtorkin Sof'ya A. Korchagina Pavel D. Komarov Alexey A. Vinogradov Andrei V. Churakov Ilya E. Nifant'ev Mikhail E. Minyaev 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(1):93-103
The crystal structures of three unusual chromium organophosphate complexes have been determined, namely, bis(μ‐butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl hydrogen phosphato‐κO:κO′)di‐μ‐hydroxido‐bis[(butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl hydrogen phosphato‐κO)(butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl phosphato‐κO)chromium](Cr—Cr) heptane disolvate or {Cr2(μ2‐OH)2[μ2‐PO2(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO:κO′]2[PO2(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO]2[HOPO(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO]2}·2C7H16, [Cr2(C19H32O4P)4(C19H33O4P)2(OH)2]·2C7H16, denoted ( 1 )·2(heptane), [μ‐bis(2,6‐diisopropylphenyl) phosphato‐1κO:2κO′]bis[bis(2,6‐diisopropylphenyl) phosphato]‐1κO,2κO‐chlorido‐2κCl‐triethanol‐1κ2O,2κO‐di‐μ‐ethanolato‐1κ2O:2κ2O‐dichromium(Cr—Cr) ethanol monosolvate or {Cr2(μ2‐OEt)2[μ2‐PO2(O‐2,6‐iPr2‐C6H3)2‐κO:κO′][PO2(O‐2,6‐iPr2‐C6H3)2‐κO]2Cl(EtOH)3}·EtOH, [Cr2(C2H5O)2(C24H34O4P)3Cl(C2H6O)3]·C2H6O, denoted ( 2 )·EtOH, and di‐μ‐ethanolato‐1κ2O:2κ2O‐bis{[bis(2,6‐diisopropylphenyl) hydrogen phosphato‐κO][bis(2,6‐diisopropylphenyl) phosphato‐κO]chlorido(ethanol‐κO)chromium}(Cr—Cr) benzene disolvate or {Cr2(μ2‐OEt)2[PO2(O‐2,6‐iPr2‐C6H3)2‐κO]2[HOPO(O‐2,6‐iPr2‐C6H3)2‐κO]2Cl2(EtOH)2}·2C6H6, [Cr2(C2H5O)2(C24H34O4P)2(C24H35O4P)2Cl2(C2H6O)2]·2C6H6, denoted ( 3 )·2C6H6. Complexes ( 1 )–( 3 ) have been synthesized by an exchange reaction between the in‐situ‐generated corresponding lithium or potassium disubstituted phosphates with CrCl3(H2O)6 in ethanol. The subsequent crystallization of ( 1 ) from heptane, ( 2 ) from ethanol and ( 3 ) from an ethanol/benzene mixture allowed us to obtain crystals of ( 1 )·2(heptane), ( 2 )·EtOH and ( 3 )·2C6H6, whose structures have the monoclinic P21, orthorhombic P212121 and triclinic P space groups, respectively. All three complexes have binuclear cores with a single Cr—Cr bond, i.e. Cr2O6P2 in ( 1 ), Cr2PO4 in ( 2 ) and Cr2O2 in ( 3 ), where the Cr atoms are in distorted octahedral environments, formally having 16 ē per Cr atom. The complexes have bridging ligands μ2‐OH in ( 1 ) or μ2‐OEt in ( 2 ) and ( 3 ). The organophosphate ligands demonstrate terminal κO coordination modes in ( 1 )–( 3 ) and bridging μ2‐κO:κO′ coordination modes in ( 1 ) and ( 2 ). All the complexes exhibit hydrogen bonding: two intramolecular Ophos…H—Ophos interactions in ( 1 ) and ( 3 ) form two {H[PO2(OR)2]2} associates; two intramolecular Cl…H—OEt hydrogen bonds additionally stabilize the Cr2O2 core in ( 3 ); two intramolecular Ophos…H—OEt interactions and two O…H—O intermolecular hydrogen bonds with a noncoordinating ethanol molecule are observed in ( 2 )·EtOH. The presence of both basic ligands (OH? or OEt?) and acidic [H(phosphate)2]? associates at the same metal centres in ( 1 ) and ( 3 ) is rather unusual. Complexes may serve as precatalysts for ethylene polymerization under mild conditions, providing polyethylene with a small amount of short‐chain branching. The formation of a small amount of α‐olefins has been detected in this reaction. 相似文献